Electrophysiology of the marine diatom Coscinodiscus wailesii - I. Endogenous changes of membrane voltage and resistance

Double-barrelled micropipettes have been used to record the endogenous elec trical behaviour of the marine diatom Coscinodiscus wailesii, diameter abou t 250 mu m, surface area about 0.2 mm(2). The conclusion is that the membra ne is not in a genuine steady-state but rather the membrane changes spontan eously between several characteristic modes, There are periods of pseudo-st eady-state in which the membrane voltage is rather stable in the range betw een -60 and -90 mV over about 1 h, and stable resistances can be found betw een 0.1 and 1.0 M Ohm. Dynamic stages are also characteristic: various type s of oscillations (sinusoidal, saw-tooth and complex non-linear) with paral lel and antiparallel phase relations between voltage and resistance, as wel l as transient voltage excursions down to -165 mV, revealing the operation of an electrogenic pump. The observed phenomena may be interpreted in terms of an electrical equivalent circuit with three parallel limbs: an electrog enic pump with a linear conductance, a K+ pathway with saturating currents of about -400 and +50 nA, and a linear Cl- conductance, each with a stable electromotive force and a variable proportion of activity.